Wireless communication systems can include a network of one or more access points (AP) to communicate with one or more wireless stations (STA). An access point can emit radio signals that carry management information, control information or users' data to one or more wireless stations, and a station can also transmit radio signals to the access point in the same frequency channel via time division duplexing (TDD) or in different frequency via frequency division duplexing (FDD).
IEEE 802.11 is an asynchronous time division duplexing technology designated for wireless local area network (WLAN) over the unlicensed spectrum. The basic unit of WLAN is a basic service set (BSS). The infrastructure BSS is the BSS with stations through associating with an Access Point (AP) to connect to the wired intranet or Internet. In a BSS, both access point and stations share the same frequency channel via using Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) technology, a kind of TDD mechanism, for multiple access and data transmission.